If the speed of the wind is w mph, the overall speed with the wind is 10+w and against it is 10-w.

The time taken to ride 4 miles in each direction is 4/(10+w)+4/(10-w)=1 because time=distance/speed.

Multiply through by (10-w)(10+w): 4(10-w)+4(10+w)=100-w².

So 40+40=100-w², w²=20, w=√20=2√5=4.472 mph.

- All categories
- Pre-Algebra Answers 12,323
- Algebra 1 Answers 25,303
- Algebra 2 Answers 10,448
- Geometry Answers 5,189
- Trigonometry Answers 2,642
- Calculus Answers 6,028
- Statistics Answers 3,026
- Word Problem Answers 10,140
- Other Math Topics 6,678

81,777 questions

86,081 answers

2,216 comments

69,578 users